EPID Portal Dosimetry Agenda
EPID Portal Dosimetry Agenda
EPID Portal Dosimetry Agenda
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<strong>EPID</strong><br />
<strong>Portal</strong> <strong>Dosimetry</strong><br />
Peter Tobe<br />
Product Marketing<br />
Varian Medical Systems<br />
December 2011<br />
Varian Confidential<br />
<strong>Agenda</strong><br />
• Philosophy<br />
• Configuration Workflow<br />
• Gamma Analysis y<br />
• Evaluation<br />
• Shortcomings & Solutions<br />
Varian Confidential<br />
Philosophy<br />
Eclipse<br />
Pre-treatment<br />
verification<br />
plan<br />
Treatment machine<br />
<strong>Portal</strong> <strong>Dosimetry</strong> Application<br />
Prediction Acquisition<br />
Varian Confidential<br />
<strong>EPID</strong><br />
06/01/2012<br />
1
Measurement<br />
Output sfactors Measured OFs<br />
AIDA Pattern<br />
P = AIDA Meas<br />
N Normalization factor<br />
SAD Source-Axis Distance<br />
SDD Source-Detector Distance<br />
FXY Open field fluence<br />
k Detector response function<br />
Configuration<br />
Workflow<br />
Varian Confidential<br />
Varian Confidential<br />
Eclipse Configuration<br />
Intensity Prof. ν<br />
f �x, y��<br />
v�rx,<br />
y �<br />
f '�x,<br />
y��<br />
N<br />
f’ =AIDA actual,corr<br />
PDIP configuration<br />
2<br />
� SAD � OF<br />
P � f '�k<br />
��<br />
� �<br />
� SDD �<br />
Varian Confidential<br />
XY<br />
�FXY � k�CAX<br />
Eclipse<br />
f= AIDA actual<br />
06/01/2012<br />
2
Detector response function<br />
Eclipse Configuration<br />
• Sum of Gaussians of different amplitude and<br />
size<br />
• Number of Gaussian components set typically<br />
to 10<br />
Varian Confidential<br />
Hardware Configuration<br />
Diagonal<br />
Beam<br />
Profile<br />
(Water Phantom)<br />
Positional<br />
Calibration<br />
Dark/Flood Field<br />
Calibration<br />
Dosimetric Calibration<br />
Beam Profile<br />
Correction<br />
Dose<br />
Normalization<br />
Varian Confidential<br />
Positional Calibration<br />
Positional<br />
Calibration<br />
• Align <strong>EPID</strong> center with iso-center using<br />
front pointer (98.8cm to imager surface)<br />
• Store preset imager position<br />
Varian Confidential<br />
06/01/2012<br />
3
Dark Field<br />
Calibration<br />
Image calibration<br />
• Integrated image mode for dosimetry<br />
• 40x32cm2 open field @ SDD=100cm<br />
Diagonal<br />
Beam<br />
Profile<br />
(Water Phantom)<br />
Flood Field<br />
Calibration<br />
Varian Confidential<br />
Dosimetric Calibration<br />
Dosimetric Calibration<br />
Beam Profile<br />
Correction<br />
Dose<br />
Normalization<br />
• Calibrate acquisition modes for all used<br />
dose rates and energies<br />
• Select diagonal beam profile for beam<br />
profile correction<br />
Varian Confidential<br />
Gamma<br />
Analysis<br />
Varian Confidential<br />
• 10x10cm2 open field @ SDD=100cm using<br />
100MU<br />
• Define <strong>EPID</strong> to dose normalization factor in<br />
calibration units [CU]<br />
06/01/2012<br />
4
Gamma Analysis<br />
Available in absolute and relative mode:<br />
• Quantitative evaluation of dose images<br />
• Factors both spatial and dose differences<br />
• User-defined pass/fail parameters<br />
• Dose Difference (Δ D)<br />
• Distance Distance-to-Agreement to Agreement (DTA)<br />
• Gamma index<br />
•0
Area Gamma vs. ROI<br />
Area Gamma Region of Interest<br />
Varian Confidential<br />
Influence of ROI on Area Gamma<br />
Varian Confidential<br />
No ROI<br />
Field + x Margin<br />
Field<br />
CIAO<br />
% Threshold<br />
Image courtesy from Institute for Radiation Oncology - Luzerner Kantonsspital<br />
Clinical Example I<br />
Varian Confidential<br />
Image courtesy from Institute for Radiation Oncology - Luzerner Kantonsspital<br />
06/01/2012<br />
6
Image courtesy from<br />
Institute for Radiation<br />
Oncology - Luzerner<br />
Kantonsspital<br />
Clinical Example II<br />
Varian Confidential<br />
Shortcomings &<br />
Solutions<br />
Varian Confidential<br />
Shortcomings<br />
• Beam profile correction<br />
• Backscatter from support arm<br />
• Cumbersome calibration<br />
procedure<br />
Varian Confidential<br />
06/01/2012<br />
7
Shortcomings: Beam profile correction<br />
Assumption: Rotationally symmetric beam profile<br />
Configuration: Use diagonal beam profile of 40x40cm 2 field<br />
to create 2D beam profile correction<br />
Issue: Correction derived from 40x40cm2 diagonal profile measured<br />
in water does not describe beam profile of 40x30cm2 field<br />
measured easu ed by imager age<br />
Gamma map of 30x20cm 2 open field<br />
Gamma (10x10cm 2 open)<br />
10x10cm 2 open<br />
30x30cm 2 open<br />
Varian Confidential<br />
Prediction<br />
Measurement<br />
Standard configuration Pre-configuration package<br />
Prediction<br />
Measurement<br />
Varian Confidential<br />
Shortcomings – Arm Backscatter<br />
Support Arm<br />
<strong>EPID</strong><br />
• Backscatter effect is field size dependent<br />
• Flood field correction inherently corrects for backscatter<br />
from 40x30cm2 field<br />
� Overcorrection for smaller fields<br />
Varian Confidential<br />
Non-uniform <strong>EPID</strong> image<br />
06/01/2012<br />
8
Gamma (10x10cm 2 open)<br />
10x10cm 2 open<br />
30x30cm 2 open<br />
Standard configuration Pre-configuration package<br />
Varian Confidential<br />
Prediction<br />
Measurement<br />
Solutions<br />
• Components & Installation:<br />
• Package will be available per energy and per machine type<br />
• Prediction:<br />
� Pre‐configured PDIP algorithm<br />
�� Simple import into Eclipse<br />
• Acquisition:<br />
� Generic 2D beam profile correction including backscatter correction<br />
� Standard dark/flood field and dosimetric calibration<br />
Varian Confidential<br />
Thank You<br />
Varian Confidential<br />
06/01/2012<br />
9
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